mxc nand: Access all ecc_status_result fields

On the NFC IP 1.1, the 32-bit ecc_status_result value comes from 2
consecutive 16-bit registers. This patch reads all the fields of this value,
which makes a difference for 4-kiB NF pages.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Cc: Scott Wood <scottwood@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Signed-off-by: Scott Wood <scottwood@freescale.com>